Process For Purifying Thioctic Acid in Water
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example 1
Repeat of Example 1 from the Degussa Patent
[0024]30 g (0.145 moles) of thioctic acid are suspended in 1000 ml of water at 20° C. 19.4 g of 30% aqueous sodium hydroxide (0.145 moles) are added drop-wise over a 1 hour period to obtain a solution at pH 9. The solution is filtered under vacuum through a paper filter and cooled to 0-3° C.
[0025]5% aqueous hydrochloric acid is added drop-wise over a 30 minute period until pH 1 is achieved, to obtain precipitation of the product.
[0026]The solid is filtered off and washed with water until the wash water is at neutral pH.
[0027]The wet product is dried at 30-35° C. for 18 hours to provide 27.9 g of solvent-free thioctic acid.
[0028]Test of solubility in chloroform (1 g in 10 ml of chloroform): cloudy solution with traces of polymer (undissolved lumps of various dimensions).
example 2
Acidifying to pH 5.4 with HCl
[0029]30 g (0.145 moles) of thioctic acid are suspended in 1000 ml of water at 20° C. 20 g of 30% aqueous sodium hydroxide (0.15 moles) are added drop-wise over a 1 hour period to obtain a solution at pH 9. The solution is filtered under vacuum through a paper filter and cooled to 5° C.
[0030]5% aqueous hydrochloric acid is added drop-wise over a 30 minute period until pH 5.4 is achieved, to obtain precipitation of the product.
[0031]The solid is filtered off and washed with water until the wash water is at neutral pH.
[0032]The wet product is dried at 30-35° C. for 18 hours to provide 24.7 g of solvent-free thioctic acid.
[0033]Test of solubility in chloroform (1 g in 10 ml of chloroform): opalescent solution with traces of polymer (undissolved lumps of various dimensions).
example 3
Acidifying to pH 2 with 5% H2SO4
[0034]15 g (0.073 moles) of thioctic acid are suspended in 500 ml of water at 20° C. 10 g of 30% aqueous sodium hydroxide (0.073 moles) are added drop-wise over a 1 hour period to obtain a solution at pH 9. The solution is filtered under vacuum through a paper filter and cooled to 5° C.
[0035]5% aqueous sulfuric acid is added drop-wise over a 90 minute period until pH 2 is achieved, to obtain precipitation of the product.
[0036]The solid is filtered off and washed with water until the wash water is at neutral pH.
[0037]The wet product is dried at 30-35° C. for 18 hours to provide 13.5 g of solvent-free thioctic acid.
[0038]Test of solubility in chloroform (1 g in 10 ml of chloroform): opalescent solution with traces of polymer (undissolved lumps of various dimensions).
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